1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, and more particularly to an electrophotographic photosensitive member having a photosensitive member containing a polymethine compound of specific structure.
2. Related Background Art
Known electrophotographic photosensitive members using an organophotoconductive material include those using a photoconductive polymer such as poly-N-vinylcarbazol or a low molecular weight, organophotoconductive material such as 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole, or those using combinations of the organophotoconductive material with various dyes or pigments.
An electrophotographic photosensitive member containing an organophotoconductive material has advantages such as a good film formability, a capability to form a photosensitive layer by coating, a very high productivity and low cost. It has a further advantage such as a free control of color sensitivity upon selection of a sensitizer to be used, such as dyes or pigments, and has been widely studied. Particularly with recent developments of the function-separated type photosensitive member based on a lamination of a charge generation layer containing an organophotoconductive dye or pigment and a charge transports layer containing the above-mentioned photoconductive polymer or low molecular weight, organoelectroconductive material, considerable improvements have been made on the sensitivity and durability, which have been regarded as disadvantages of the conventional organic electrophotographic photosensitive members.
A polymethine coloring matter has a methine chain connected with a conjugated double bond within a molecule and thus has an absorption range extending from the visible to the near infrared zone by .pi.--.pi.* transition. Thus, intense development has been made on the ground of the functional coloring matter, and a large number of compounds have been so far proposed. For example, squarium pigment, [Japanese Patent Application Laid-open No. 62-450, etc.], cyanine coloring matter [Japanese Patent Application Laid-open Nos. 57-188043 and 59-49546] are well known. However, generally the conventional polymethine pigment has a low light resistance and it is often not satisfactory in potential stability when repeatedly used. Its practical application is limited, for example, to recording materials, etc.